neutralisation
•In neutralisation, the acidity of an acid is neutralised by alkali.
•At the same time, the alkalinity of the alkali is neutralised by the acid.
•The hydrogen ions in the acid will react with hydroxide ions in the alkali to produce water.
Acid-Base Titration
Titration
Quantitative analysis that used to determine the volume of an acid needed to neutralise completely of a known volume and concentration of an alkali with the help of an indicator
End Point
Is the point in the titration at which the indicator changes color.
In acid-base titration:
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Volume of an alkali is measured accurately using a pipette and is poured into a conical flask
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A few drops of indicator is added into the alkali solution to show the end point
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The acid solution from the burette is added slowly into the conical flask until the color of mixture in the conical flask changed.
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End point occur when complete neutralisation is occurring, that is certain volume of acid is needed to neutralize completely a known volume of an alkali
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Ø The color of indicator is different in different solutions as shown in the table:
Question 1:
25.0 cm3 of sulphuric acid is neutralised by 34.0 cm3 of 0.1 mol of dm-3 NaOH. Calculate the concentration of sulphuric acid in:
a)mol dm-3
b)g dm-3
[relative atomic mass; H:1, S:32, O:16]
Solution:
Method 1
Step 1: write down chemical equation
NaOH + H2SO2 Na2SO4 + H2O
Step 2: find the number of mole NaOH
n=MV
Moles of NaOH
=molarity X Volume (dm3)
=0.1 X 0.034
=0.0034 mol
Step 3: from the chemical reaction, the ratio of
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Step 4: find the number of moles of H2SO4
Reacted
2 mole of NaOH= 1 mole of H2SO4
0.0034 mole of NaOH = ((0.0034 X 1)/2) mol
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Method 2:
Step 1: write down chemical equation
NaOH + H2SO2 Na2SO4 + H2O
Step 2: find the concentration of H2SO4 in mol dm-3
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Step 3: find the concentration of H2SO4 in g dm-3
Molar mass H2SO4 = 1(2) + 32 + 16 (4)
= 98 mg mol
Concenration= concentration in mol dm-3 X molar mass H2SO4
=0.068 X 98
= 6.664 g dm-3
Application of neutralisation
Insect stings
•Insect Stings Bee stings are acidic and can be neutralised with baking soda (bicarbonate of soda). Wasp stings are alkaline and can be neutralised with vinegar.
Indigestion
•Our stomach carries around hydrochloric acid. Too much of this leads to indigestion. To cure indigestion, you can neutralise the excess acid with baking soda or specialised indigestion tablets.
Soil treatment
•When soils are too acidic (often as a result of acid rain) they can be treated with slaked lime, chalk or quicklime, all alkalis. Plants and crops grow best in neutral soils
Factory Waste
•Liquid waste from factories is often acidic. If it reaches a river it will destroy and kill sea life of many forms. Neutralising the waste with slaked lime can prevent this.
